Touch Sensing Circuit With Common-Mode Filtering for Parasitic Capacitance
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Solution Overview
Problem
The presence of parasitic capacitance in touch sensing devices, particularly in pOLED displays, leads to reduced touch sensitivity and signal noise ratio degradation, making it difficult to design effective sensing amplifiers and increasing the design area of touch sensing devices.
Innovation Solution
A touch sensing device is designed with buffers, current mirror units, filter circuits, and integrators to buffer and process signals, removing common noise and enhancing signal quality by directly connecting touch sensing lines to buffers and using cascode configurations in output circuits and current mirror units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a touch screen panel is embedded into a display panel, then integration and compactness are improved, but parasitic capacitance increases between touch driving patterns and peripheral conductors
Solution Approach 1:
A common mode filter circuit is introduced as an intermediary component between the touch sensing lines and the sensing amplifier. This filter circuit specifically targets and removes common mode noise signals caused by parasitic capacitance, allowing the embedded touch screen panel to maintain high integration while mitigating the harmful parasitic capacitance effects through active noise filtering.
Solution Approach 2:
The patent implements a feedback mechanism where the common mode filter circuit continuously monitors and processes the differential signals from the touch sensing lines. By detecting common mode noise components and actively compensating for them through the filter circuit, the system creates a feedback loop that dynamically counteracts the parasitic capacitance effects, enabling stable touch sensing performance in the embedded configuration.
2Length of moving object
If parasitic capacitance increases between touch screen panel and cathode electrode, then touch sensitivity is reduced, but device thickness is thinned
Solution Approach 1:
The common mode filter circuit serves as a mediator that processes the touch sensing signals after they pass through the thinned device structure. By filtering out the common mode noise generated by parasitic capacitance between the touch screen panel and cathode electrode, the filter circuit preserves touch sensitivity despite the reduced device thickness that increases parasitic coupling.
Solution Approach 2:
The patent converts the harmful effect of parasitic capacitance into a detectable common mode noise signal that can be systematically removed. By recognizing that parasitic capacitance generates predictable common mode noise, the system uses the common mode filter circuit to identify and eliminate this noise, thereby transforming the harmful parasitic effect into a manageable signal characteristic that can be filtered out to preserve touch sensitivity.
3Reliability
If feedback capacitor is increased to compensate for parasitic capacitance, then touch sensing performance is maintained, but design area increases
Solution Approach 1:
The common mode filter circuit is introduced as an intermediary that handles noise removal separately from the main sensing amplifier design. This allows the sensing amplifier to use smaller feedback capacitors while the filter circuit independently manages the parasitic capacitance effects through common mode noise filtering, thereby maintaining touch sensing performance without requiring large feedback capacitors that would increase the design area.
4Device complexity
If parasitic capacitance is present, then signal noise ratio degrades, but device complexity is reduced
Solution Approach 1:
The common mode filter circuit acts as an intermediary noise removal stage that sits between the touch sensing lines and the sensing amplifier. This dedicated filter circuit specifically targets common mode noise from parasitic capacitance, improving signal noise ratio without requiring complex modifications to the overall device architecture, thereby maintaining relatively simple device complexity while effectively combating noise degradation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution improves touch sensing performance by reducing the impact of parasitic capacitance, maintaining high signal noise ratio, and simplifying amplifier design, while minimizing the design area and signal degradation.
Implementation Method 1
a first current mirror unit connected to the first buffer to generate a first mirror current by performing a mirroring operation on a first current flowing in the first pull-up circuit and to generate a third mirror current by performing a mirroring operation on a second current flowing in the first pull-down circuit
Data Source
AI summary
Disclosed is a touch sensing device for preventing touch sensing performance from being reduced by a parasitic capacitance. The touch sensing device includes a plurality of buffers buffering a difference between a reference signal and a reception signal received from a touch electrode through a touch sensing line and generating first and second currents corresponding to a buffered signal, a plurality of current mirror unit respectively connected to the plurality of buffers, a plurality of filter circuits generating a first filter signal and a second filter signal by removing common noise included in a first output signal output from an nth current mirror unit of the plurality of current mirror units and a second output signal output from an (n−1)th current mirror unit of the plurality of current mirror units, and a plurality of integrators respectively connected to the plurality of filter circuits.